Computer networks, particularly those with global reach such as the Internet, have greatly influenced the way transactions are conducted and the way data is stored and retrieved. With the growth of the Internet, user authentication has become increasingly important for both computer systems and networks. Secure access to computer systems and computer networks has been traditionally implemented using a user identification (userid) and password pair. This requires the user to protect their userid and password from unauthorized use. If the userid and password are not protected, accounts and files can be compromised. For example, if a first user knows the userid and password of a second user, then the first user may easily access the second user's account information without being authorized to do so.